Applications for gel quality attapulgite in “drilling” include oil and gas well drilling, foundation and footing construction drilling and trenching for environmental containment but with oil and gas well drilling constituting the largest global drilling market.
When drilling deep wells for oil and gas, the hole is kept continually filled with a fluid mud slurry. The mud suspends the cuttings which are then removed as it is recirculated through a de-sander or screen. The mud cools and lubricates the drill bit and also forms a filter cake which helps reduce fluid loss. Because of its unique properties, AMI’s gel quality attapulgite is used mainly in saltwater and seawater drilling.
Gel quality attapulgite was developed by AMI’s predecessor company, Floridin, decades ago specifically for salt water drilling due to the poor performance of bentonite clay in salt water applications. Many customers simply call it “salt gel” because it works in salt water and in drilling fluids whenever ionic contamination from materials such as salts, gypsum, sea water, or cement are encountered or anticipated.
During mechanical mixing with the makeup water, the clay’s particles are dispersed and interact with each other to form a stable gel structure throughout the liquid. Due to this clay’s special properties, the makeup water used may be fresh, brackish, saturated with salt, or it may contain gypsum or cement.
Foundation Drilling and Trenching Using the Clay Slurry Method
Drilling or trenching is often necessary in construction of reinforced concrete foundations for bridges, various tower applications, and cut-off walls. The slurry method is frequently used in sandy soils with high water tables. As the hole or trench is opened, it is kept filled with clay slurry. Its function is to keep the hole or trench from collapsing by providing a more stable, uniform and higher density fluid in the cavity, than the surrounding groundwater; form a cake or seal the cavity walls, reducing fluid loss into the surrounding formation, and to suspend materials so they do not settle to the bottom of the hole or trench.
For structural foundations, after the reinforcement is placed, the slurry is either pumped or forced out by the concrete as it is tremied into the hole or trench.
For in-ground environmental cut-off walls the slurry may be left in the ground indefinitely so the slurry must have sufficient density to prevent the walls from sloughing or collapsing, sufficient viscosity to keep the clay in suspension and a viscosity low enough to enable pumping of the slurry over some distances. Yield stress of the slurry must be high enough to suspend sand particles and all of these characteristics must not change on aging of the slurry.
AMI produces and markets high quality attapulgite clays used to formulate these slurries. They offer several benefits compared to other materials, including formation of slurries in fresh water with a lower clay concentration, formation of stable slurries in salt water and formation of slurries with higher gel strength and better suspending ability.